arch/x86/purgatory/purgatory.c

   1 /*
   2  * purgatory: Runs between two kernels
   3  *
   4  * Copyright (C) 2014 Red Hat Inc.
   5  *
   6  * Author:
   7  *       Vivek Goyal <vgoyal@redhat.com>
   8  *
   9  * This source code is licensed under the GNU General Public License,
  10  * Version 2.  See the file COPYING for more details.
  11  */
  12
  13 #include <linux/bug.h>
  14 #include <linux/sha256.h>
  15 #include <asm/purgatory.h>
  16
  17 #include "../boot/string.h"
  18
  19 unsigned long purgatory_backup_dest __section(.kexec-purgatory);
  20 unsigned long purgatory_backup_src __section(.kexec-purgatory);
  21 unsigned long purgatory_backup_sz __section(.kexec-purgatory);
  22
  23 u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE] __section(.kexec-purgatory);
  24
  25 struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX] __section(.kexec-purgatory);
  26
  27 /*
  28  * On x86, second kernel requries first 640K of memory to boot. Copy
  29  * first 640K to a backup region in reserved memory range so that second
  30  * kernel can use first 640K.
  31  */
  32 static int copy_backup_region(void)
  33 {
  34         if (purgatory_backup_dest) {
  35                 memcpy((void *)purgatory_backup_dest,
  36                        (void *)purgatory_backup_src, purgatory_backup_sz);
  37         }
  38         return 0;
  39 }
  40
  41 static int verify_sha256_digest(void)
  42 {
  43         struct kexec_sha_region *ptr, *end;
  44         u8 digest[SHA256_DIGEST_SIZE];
  45         struct sha256_state sctx;
  46
  47         sha256_init(&sctx);
  48         end = purgatory_sha_regions + ARRAY_SIZE(purgatory_sha_regions);
  49
  50         for (ptr = purgatory_sha_regions; ptr < end; ptr++)
  51                 sha256_update(&sctx, (uint8_t *)(ptr->start), ptr->len);
  52
  53         sha256_final(&sctx, digest);
  54
  55         if (memcmp(digest, purgatory_sha256_digest, sizeof(digest)))
  56                 return 1;
  57
  58         return 0;
  59 }
  60
  61 void purgatory(void)
  62 {
  63         int ret;
  64
  65         ret = verify_sha256_digest();
  66         if (ret) {
  67                 /* loop forever */
  68                 for (;;)
  69                         ;
  70         }
  71         copy_backup_region();
  72 }